1. Field of the Invention
The present invention relates to an open loop pressure regulation method for a respiratory assistance apparatus, and to a compression device of a compression apparatus for implementing this method.
2. Description of the Related Art
The problem encountered with respiratory assistance apparatuses which are required to supply a variable air flow rate at constant pressure is that of the response time. It is in fact necessary to succeed in producing an endotracheal reference pressure which can be adjusted by the practitioner, which is independent of the instantaneous inhalation flow rate demanded by the patient, the exhalation passing through an exhalation valve, the inhalation valve then being closed.
There are two types of respiratory assistance apparatuses. The apparatuses of the first type comprise a pressurized respiratory gas supply, the flow rate and the pressure of which are regulated by a regulating valve with a variable constriction. The apparatuses of the second type have no pressurized gas supply, but a compressor with variable pressure and flow rates.
Existing apparatuses operate with pressure feedback, which requires a compromise between stability of the closed-loop system and its response time. The response time of such systems is about 50 to 150 ms, while the response time of the valve is about 4 to 10 ms.
It would not be possible to operate in open-loop mode with such a system, given the friction which is not a fixed parameter and the measurement of which would be too complex. To operate in open-loop mode, it is therefore first of all essential to find a compression device operating virtually without mechanical friction. FR-2733688 has already proposed a respiratory assistance apparatus whose pressurized gas source is a compressor with an electromagnetically actuated membrane. This compressor comprises a casing which contains two chambers of variable volume having a guide shaft which passes through a soft iron core placed coaxially at the center of an annular magnet and which bears at each of its ends a rigid circular plate fitted with an annular membrane, the periphery of which is fastened to the inner wall of the casing, thus defining, inside the casing, two chambers, the respective volumes of which vary according to the displacement of the plates and membranes. Each chamber comprises at least one inlet valve and at least outlet valve in order to control the inlet and outlet of the air.
Such a compression device does not meet the requirements of a system operating in open-loop mode, given that the guide shaft is a significant source of friction.
The aim of the present invention is to make it possible to provide a solution to regulating a respirator comprising a membrane compressor, so that its response time is reduced virtually to that of the membrane of the compression device.
To this end, the subject of the present invention is first of all a method of regulating, in open-loop mode, a respiratory assistance apparatus, as claimed claim 1. The subject of the invention is also a respiratory assistance apparatus as claimed in claim 3.
The advantage of this method and of the apparatus for its implementation arises from the fact that in the absence of mechanical friction, it is enough to measure the flow rate and to know the reference pressure in order to calculate the instantaneous supply current of the driving coil, the other parameters consisting of the constants of the respiratory assistance apparatus.
The appended drawing illustrates, schematically and by way of example, one embodiment of the respiratory assistance apparatus for implementing the method which is the subject of the present invention.